Field of the Invention
This invention relates to a color television camera in which the image pickup tube is illuminated by an auxiliary illumination source or a bias light source to eliminate the residual image.
This television camera is classified into two types by the position of the auxiliary illumination source: the first type, in which the auxiliary illumination source is positioned in front of the incidence surface of the color separation prism, and the second type, in which the auxiliary illumination source is positioned behind the incidence of the color separation prism. As the typical example of the first type, there is a television camera described in U.S. Pat. No. 3,767,846. The television camera of this U.S. patent has an auxiliary light source device including the light guide rod arranged between the objective lens and a color separation prism. The light coming from this light source device illuminates the image pickup tube by illuminating the incidence surface of the color separation prism.
As the second type, there is a television camera described in U.S. Pat. No. 3,610,818. This television camera has a light source arranged behind the incidence surface of the prism. The light coming from the light source is transmitted through the sub-prism cemented on the color separation prism and enters the color separation prism, and after being reflected by a dichroic layer and total reflecting surfaces, the light illuminates the image pickup tube. However, in this television camera, since the auxiliary illuminating light enters the image pickup tube at a definite angle, this television camera has a fault that the amount of illuminating light is not constant.
In the U.S. Pat. No. 3,824,004, a television camera free from the above-mentioned fault is shown. In this U.S. patent, this television camera has a sub-prism cemented with the color separation prism, and in which a part of the light coming from the auxiliary light source and transmitted through the incidence surface of this sub-prism is directed to the image pickup tube by the reflecting surface of the sub-prism and a mirror positioned on the incidence surface of the color separation prism. The other part of the light is directed to said image pickup tube by being reflected on the tilted mirror facing to the incident surface of said sub-prism. In this camera, the incident angles of the two auxiliary illuminating light beams are symmetrical to each other with respect to the normal axis of the surface of the image pickup tube. Accordingly the above-mentioned fault that the amount of illuminating light is not constant is removed. However, this television camera has a complicated construction with use of a sub-prism. Then, this television camera has the fault that the article costs high.